Phase 5: group-voice docs, onboarding runbook, CHORUS icon — v2.0.0-rc.1

The final phase of CHORUS-PLAN.md. Code- and doc-complete for group use;
rc pends live deployment at chorusapi.mpm.to.

- Repo README rewritten for CHORUS: group model (schema 5), concurrency
  posture, configuration, baked-build onboarding, layout, testing, 2.0
  version history (ECHO history referenced at the fork tag).
- Operator→member voice sweep across SKILL.md (incl. the trigger
  description, now group-aware), all references, 8 command docs, plugin
  README; member preferences / semantic layer / triage guidance describe
  the group model.
- docs/ONBOARDING.md: member runbook — vault stand-up, per-member config,
  bake, deliver, self-onboarding first load, norms, offboarding.
- docs/USAGE.md rewritten as the member usage guide.
- New icon: chorus-icon.svg + 1024/512/64 PNGs (three voices, one center).
- Removed ECHO-era assets (icons, spec PDF, perf briefs); ECHO planning
  docs retired to docs/history/. All preserved at echo-fork-point.
- eval/README documents test_multimember.py. Manifest -> 2.0.0-rc.1;
  rebuilt chorus-memory.plugin.

Verified: routing-sync, 25/25 unit, scaffold, 5 mock e2e suites,
run_eval metrics green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

chorus-memory.plugin.src/commands/chorus-sweep.md

@@ -3,7 +3,7 @@ description: Bring the CHORUS vault up to the current feature spec (entity index
 allowed-tools: Bash(python3 *sweep.py*), Bash(python *sweep.py*), Bash(ls /sessions/*), Bash(dirname *)
 ---
 
-Use the **chorus-memory** skill to bring the vault up to the current spec. Run the sweep **dry-run first**, show the operator the plan, and only `--apply` on their go-ahead:
+Use the **chorus-memory** skill to bring the vault up to the current spec. Run the sweep **dry-run first**, show the member the plan, and only `--apply` on their go-ahead:
 
 ```bash
 SDIR="${CLAUDE_PLUGIN_ROOT}/skills/chorus-memory/scripts"